To produce hardening multi-component impression compounds for use in dentistry, components are employed which are contained in cylindrical cartridges and which are pressed out synchronously and mixed together (EP 87 029 A1, EP-A-492 413, WO98/44860). The cartridges are designed as storage cylinders whose front ends form nozzle openings, which are each connected to an inlet opening of a mixing nozzle, and whose rear ends are open for receiving a plunger which is advanced inside the cylinder in order to press out the compound. To do this, equipment is used into which the cartridges connected to or to be connected to the mixing nozzle are introduced, and which has, for each cartridge, a stamp which acts on its plunger by way of the rear open end of the cartridge. To achieve a constant mixing ratio, the stamps are mechanically connected to one another for synchronous movement and are provided with a common electric drive mechanism. The latter comprises a coupling which can be released so that the stamps can be withdrawn from the cartridges by hand if they are to be changed. This change takes place if the cartridges are empty or if the type of impression compound is to be changed.
The mixers used are usually dynamic mixers. These are oblong, cylindrical or conical containers in which mixer vanes revolve and to whose one end the components to be mixed are delivered, and from whose other end the mixed compound emerges through a nozzle opening. At the delivery end of the container, the mixer shaft is equipped with a coupling part which, with the complementary coupling part of a drive shaft provided in the equipment, forms a coupling which is closed by attachment of the mixer to the equipment. Instead of a dynamic mixer with revolving mixer vanes, it is also possible to use a static mixer which is connected in the same way to the equipment and in which baffle plates are arranged which effect the mixing of the components as they flow through.
Until recently, the production of impression compounds almost exclusively used components of like viscosity. When changing over to compounds whose components have a different viscosity than the conventional components, or in which the viscosities of the components to be mixed differ greatly from one another, a deterioration in mixing quality is observed, and the reaction to this is to use different mixers. The disadvantage of this is that different mixer nozzles have to be kept in stock for different multi-component compounds, and replacement of the mixer nozzles can lead to errors being made. This is not only inconvenient, but also entails the risk that poor mixing will cause uncured material to drip into the patient's pharynx or, as a result of punctiform overheating of the material, the patient may suffer burns.